The present invention relates to a device for feeding strip paper on a dual-rod cigarette manufacturing machine. On dual-rod cigarette manufacturing machines, cigarettes are usually formed by feeding two strips of paper through a filling station where a continuous layer of shredded tobacco is fed onto each strip.
Each strip of paper and the respective layer of tobacco are then fed through a forming fixture along which the opposite side edges of the strip are gradually folded together about the layer of tobacco and then stuck together to form a continuous cigarette rod which is cut into single cigarette lengths, together with the other rod, by a single cutting head turning at constant speed.
The paper strips are usually fed through the machine by means of a feed device comprising a reel-off unit for reeling off a coil a strip of paper twice the width of the said strips. The speed at which the said single strip is reeled off the coil is timed to the cutting rate of the said cutting head, in such a manner as to produce, at least theoretically, cigarettes of a given length. The said feed device also comprises a cutting unit for cutting the said single strip longitudinally into the said two strips, each of which is fed onto a respective conveyor extending along the said forming fixture and responsible for feeding the respective strip along the same. Mating of each strip on the respective conveyor only occurs in the presence of the respective layer of tobacco, which, when arranged over the paper strip, determines mechanical mating by friction between the conveyor and the respective strip.
On dual-rod cigarette manufacturing machines of the aforementioned type, after a given operating time, and particularly on account of differing wear, i.e. differing thickness, of the two conveyor belts, the two paper strips have been found to travel at different speeds and, owing to the common source of both strips, are subjected to different tensions which may lead to tearing of at least one of them.
For this reason, Italian Patent Application No. 3440A/83 filed by the present Applicant provides for means for controlling the tension of both paper strips, each of which means regulates the speed of the respective conveyor and, consequently, the speed and tension of the respective paper strip.
In actual practice, however, providing the conveyors are replaced periodically and both strips are fed along exactly the same route, the tension of both strips has been found to depart by a very limited amount and in the same direction from a given preset value.
Consequently, under normal operating conditions, the respective tensions of both strips tend to remain substantially the same, even while departing from the said given preset value.
In the light of this discovery, known devices have proved complex, expensive and, more importantly, poorly suited for meeting the requirements of such machines, at least when operated under normal conditions.